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Choose the odd number: 17, 19, and 23 are primes. One number is composite. Identify the composite number.

Difficulty: Easy

17
19
23
27
None of these

Correct Answer: 27

Explanation:

Introduction / Context:
Prime recognition again isolates the outlier.

Given Data / Assumptions:

Candidates: 17, 19, 23, 27.
Definition: prime vs composite.

Concept / Approach:
Use small-prime divisibility tests (especially 3).

Step-by-Step Solution:

27 → 2+7=9 → divisible by 3 → composite (3^3).17, 19, 23 → not divisible by 2,3,5 → primes.

Verification / Alternative check:
Direct factorization: 27 = 3 * 9 confirms compositeness.

Why Other Options Are Wrong:
They are prime.

Common Pitfalls:
Assuming all odd numbers are prime.

Final Answer:
27 is the odd number.

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